Drop on demand ink jet technology is widely used in the printing industry. Printers using drop on demand ink jet technology may use a plurality of electrostatic actuators, piezoelectric actuators, or thermal actuators to eject ink from a plurality of nozzles in an aperture plate. In electrostatic ejection, each electrostatic actuator, which is formed on a substrate assembly, typically includes a flexible diaphragm or membrane, an ink chamber between the aperture plate and the membrane, and an air chamber between the actuator membrane and the substrate assembly. An electrostatic actuator further includes an actuator electrode (i.e., drive electrode) formed on the substrate assembly. When a voltage is applied to activate the actuator electrode, the membrane is drawn toward the electrode by an electric field and actuates from a relaxed state to a flexed state, which increases a volume of the ink chamber and draws ink into the ink chamber from an ink supply or reservoir. When the voltage is removed to deactivate the actuator electrode, the membrane relaxes, the volume within the ink chamber decreases, and ink is ejected from the nozzle in the aperture plate.
One critical aspect of electrostatic actuators is the dimensions of a spacing or gap between the actuator electrode and the membrane. The gap affects both the volume of ink ejected from a nozzle upon removal of the voltage from the actuator electrode and the voltage that must be applied to the actuator electrode to sufficiently deflect the membrane to eject ink from a printhead nozzle. A gap that is too narrow or too wide will eject either an insufficient or excessive quantity of ink respectively. Further, as the gap height increases, the power that must be applied to the actuator electrode to sufficiently deflect the membrane also increases.
An electrostatic actuator further includes a dielectric gap standoff layer formed on portions of the conductive layer that is used to form the actuator electrodes. The membrane is adhered or bonded to an upper surface of the gap standoff layer with an adhesive to space the membrane from the electrode; thus a thickness of the gap standoff layer partially determines the gap between the actuator electrode and the membrane. The gap height is also affected by the technique used to bond the membrane to the gap standoff. An adhesive layer, for example EPON™ available from Miller-Stephenson Chemical Co. of Danbury, Conn., a liquid resin, a solder, or another flowable adhesive may be interposed between the gap standoff and the membrane, and then cured during the application of heat and pressure to bond the actuator membrane to the gap standoff. This process, however, is prone to contamination of the actuator air chamber (i.e., the electrostatic gap) with stray adhesive which may encroach or “squeeze out” into the actuator air chamber during the bonding of the membrane to the gap standoff under the application of heat and pressure. Excessive adhesive may negatively affect device performance, for example, if the adhesive encroaches between the membrane and the electrode. Some variation in the quantity of liquid adhesive dispensed onto the actuator membrane and/or gap standoff prior to assembly is unavoidable, and negative effects from adhesive squeeze out becomes more problematic as an excess of adhesive is applied. Further, processing variation may affect the accuracy of the final adhesive thickness and contributes to variation in the gap height away from a target height.
A method for forming an electrostatically actuated ink jet printhead that overcomes problems associated with some other formation methods, and the resulting printhead, would be desirable.